Cannot use private libs anymore

[kLabz]

Since #473, compiling with my private libs leads to this error:

Error: Error: Cannot process [xxx]: missing field license

Followed by this if I set "license": "":

Error: Error: Cannot process [xxx]: Invalid value  for License

I am now supposed to add one of these for a private lib in order to compile my project:

"GPL", "LGPL", "BSD", "Public", "MIT", "Apache"

[ibilon]

I think we should keep the full haxelib.json check, but add an "Other" value for license, and a check on upload to lib.haxe.org that it's not "Other".

[ncannasse]

That annoyed me too, I had to add a user name and a license for private libraries which didn't required it before.